Introduction
Carbohydrates play a key role in athletic performance – particularly as an energy source. Carbohydrate, in the form of glucose,
does not only fuel active skeletal muscle, but it is also a metabolic fuel for nerve cells and red blood (1). Elite athletes
and exercise physiologists do not solely view carbohydrates as a fuel source, but also study the effects that carbohydrates
have on physique/body composition. Because of advances in nutritional biochemistry, it has been learned that various types
of carbohydrates affect the body differently. Amazingly, some types of carbohydrates are preferentially converted to fat,
raise blood glucose levels to high physiologic levels, and are linked to health problems such as diabetes, obesity, cancer, etc.
(2,3,6,9). Other types of carbohydrates, such as disaccharides and polysaccharides, are not converted to fat easily and are not
considered to be deterrents to good health. Relative to dietary carbohydrate, this article will discuss the differences between
the glycemic index and the glycemic load. Because of its practical application relative to food intake, professionals in the human
performance industry should consider the glycemic load of a food when designing meals, planning recovery nutrition,
and creating specialized diets to enhance body composition.

The Glycemic Index
The glycemic index was developed by researchers from the University of Toronto approximately thirty years ago, and was
primarily used as a tool for diabetics looking to control their blood glucose (blood sugar) levels (7). Today, many other nondiabetic
individuals are also using this index as a way to choose foods to eat for health, weight loss and performance. Relative
to weight loss, several scientific studies have been conducted with the primary intervention being the glycemic index values
of various diets (4,10,11). Specifically, the glycemic index is a numerical ranking of carbohydrate-containing foods based on
their potential to raise blood sugar levels. Carbohydrates that are high on the glycemic index (>70) are quickly digested and
absorbed. These carbohydrates tend to cause a rapid rise in blood glucose and in most cases a quick rise in insulin. Conversely,
carbohydrates that are low on the glycemic index (~55 and below) are more slowly absorbed and subsequently cause
a relatively small increase in blood sugar and insulin. Hence, the glycemic index allows an individual to indirectly estimate
both blood glucose and insulin levels which is not only important for diabetics, but is also important for anyone looking to
control body weight or when determining what type of carbohydrates to ingest prior to and following exercise bouts.

Determining the Glycemic Index of a Food
Researchers measure out a portion of food that contains 50 grams of carbohydrate. For instance, 4 slices of bread, 1 1/4 cups
of rice, 1 1/2 pounds of carrots, and 2 medium apples each contains about 50 grams of available carbohydrate. A food is fed
to a group of test subjects and their blood sugar responses are measured. The test subjects’ blood sugar response to the food
is then compared with their response to eating 50 grams (about 3 tablespoons) of pure glucose. To illustrate this point, oatmeal
will be used as an example. Oatmeal on average is approximately 49 on the glycemic index. When plain oatmeal that
contains 50 grams of carbohydrate is eaten, it will produce an increase in blood sugar approximately 49% of that obtained
when the same amount (i.e. 50 grams) of straight glucose is consumed.

Foods That Have a High Glycemic Index
Generally speaking, foods that rank high on the glycemic index include products made from finely ground flours like bread
and baked goods; processed breakfast cereals (Corn Flakes®); candy (i.e., jelly beans), and baked, mashed, and French fried
potatoes (5). Foods that rank lower on the glycemic index include most vegetables and fruits; sweet potatoes; legumes; minimally
processed whole grains such as thick-cut oatmeal, oat bran, barley, pasta; and dairy products (5).

Glycemic Index vs. Glycemic Load
The glycemic index is not the only tool that can be used to determine the blood glucose response to a particular food item.
The glycemic load uses the glycemic index as well as the actual amount of carbohydrate (i.e. the serving size) to determine
the overall effect that a carbohydrate-containing food has on blood sugar and subsequent insulin values. As mentioned
earlier, the glycemic index compares different food sources that contain carbohydrates of the same quantity (i.e. 50 grams of
glucose is compared to 50 grams of carbohydrate in oatmeal). However, this is not always practical or realistic because many
foods are not consumed in 50 gram (1.76 ounces) portions. The glycemic load is calculated by multiplying the amount of
carbohydrate in a given serving of food by the glycemic index of that same food and then dividing that number by 100.
For example, a boiled potato has a glycemic index of ~101 and a Mars® candy bar has a glycemic index of ~65. However,
the average serving size of a baked potato is about 150 grams (5.3 oz) and contains 17 grams of carbohydrate. Conversely,
a Mars® candy bar serving size is only 60 grams (2.1 oz) but contains 40 grams of carbohydrate. The boiled potato has a
glycemic load of 17, while the Mars bar is 26. Thus, even though the potato has a higher glycemic index, the Mars® candy
bar has a greater effect on blood glucose than the potato even though the size of the Mars® candy bar is less than half that of
the potato. Dr. Jeukendrup, a respected sports nutrition researcher, reports that foods with a glycemic load of > 20 are high,
11-19 are medium, and < 10 are low (8). The following table lists some common foods with their corresponding glycemic
index and glycemic loads.

Conclusion
While both the glycemic index and the glycemic load provide information relative to the impact that carbohydrates have on
the blood sugar and subsequent insulin response, the glycemic load is a more practical scale for reasons mentioned above.
It is also important to realize that both glycemic index and glycemic load only refer to the food eaten alone. When fat or
protein from other foods are added to a meal containing carbohydrates, the total impact of either score goes down. In conclusion,
since carbohydrate intake and its effects on the blood glucose/insulin response are important for the hard training
athlete, one should consider utilizing the glycemic load to assist in making carbohydrate food choices.

References

Bill Campbell, PhD, CSCS

Food intolerance is a digestive system response. The immune system is not responsible for the symptoms of a food intolerance, even though these symptoms can resemble those of a food allergy. A food intolerance occurs when something in a food irritates a person's digestive system or when a person is unable to properly digest or breakdown the food.

Symptoms of food intolerance include:

• Nausea
• Stomach pain
• Gas, cramps, or bloating
• Vomiting
• Heartburn
• Diarrhea
• Headaches
• Irritability or nervousness

There are many factors that may contribute to food intolerance. In some cases, as with lactose intolerance, the person lacks the chemicals, called enzymes, necessary to properly digest certain proteins found in food. Also common are intolerances to some chemical ingredients added to food to provide color, enhance taste, and protect against the growth of bacteria. These ingredients include various dyes and monosodium glutamate (MSG), a flavor enhancer.

Substances called sulfites are also a source of intolerance for some people. They may occur naturally, as in red wines or may be added to prevent the growth of mold.

Salicylates are a group of plant chemicals found naturally in many fruits, vegetables, nuts, coffee, juices, beer, and wine. Aspirin also is a compound of the salicylate family. Of course, any food consumed in excessive quantities can cause digestive symptoms.

Ongoing research suggests that how well our metabolism functions is a key factor in weight loss or gain, and some of the foods that are most likely to trigger an intolerance are known to disrupt our metabolism. Research also shows that our metabolism works more efficiently when we eat a variety of nutrients.

It is common to crave the foods that we are intolerant to. If we don’t get our regular fix, then withdrawal symptoms may kick in, often resulting in binge eating and weight gain.

In the case of fluid retention, an offending food appears to affect the body by increasing the permeability of the capillaries (fine blood vessels), which means that extra water flows into cells. Also, abdominal bloating might be a symptom of fluid retention, or it could be a sign that the digestive system is not dealing particularly well with a specific food. Either way, excess weight is the result.

Mass food production has meant that our diet has become highly processed and contaminated with chemicals and, in the case of wheat, bears little resemblance to what our great grandmothers used when baking their daily loaf. We are generally eating more processed foods, refined sugars and additives, often eating a limited number of foods and suffering with impaired digestion. All of these factors lead to our inability to digest food properly and result in a blocked digestive system.